Actuating circuit for automatically reversing a reciprocal scanner



March 28, 1967 LE ROY E. JOHNSON 3,311,820

ACTUATING CIRCUIT FOR AUTOMATICALLY REVERSING A RECIPROGAL SCANNER Filed June 7, 1963 FIG.

INVENTOR.

LEROY E. JOHNSON TTORNEY,

United States Patent ()fiice 3,311,326 Patented Mar. 28, 1967 Filed June 7, 1963, Ser. No. 286,420 4 Claims. (Cl. 324-37) This invention relates to electrical apparatus for energizing a control device periodically in relation to the position achieved by a movable member with respect to a workpiece and wherein the member is directed and/ or controlled by fihe said device. The principal object of the invention is to provide such apparatus which is essentially of an electronic character and thus possessive of no moving parts which would detract from the applicability of the apparatus to uses requiring sustained maintenance of rapidly repetitive functions as well as the 'ability to withstand severe conditions of mill service.

While the invention herein disclosed has been developed to automatically control the length of stroke and the reversal of scanning apparatus for inspecting an outer sur face of a square or rectangular metal billet 'as the latter is advanced longitudinally along a suitable conveyor, it

should be apparent that the principles of the invention are equally applicable to other specific uses requiring comparable functions. Thus, the electrical apparatus disclosed herein is adapted for use in the billet scanning equipment disclosed and claimed in co-pending application Ser. No. 284,956, filed June 3, 1963, by John S. Miller, and assigned to the same assignee as the instant application, wherein search coils to detect defects in a flat surface of a longitudinally advancing square or rectangular billet are mounted on a reciprocating carriage for movement back and forth over a face of the billet and in a direction generally transverse to the longitudinal axis thereof.

A further object of the invention is to provide electronic control apparatus for the general purpose outlined above which is operative to automatically reverse the stroke of the scanning carriage upon the working element carried thereby reaching the side edge of the face of the billet in either direction regardless of variations in the transverse dimension of the face and of the fact that the billet has simultaneous longitudinal movement. Another object of the invention is the provision of such apparatus which does not require any mechanical devices in the position responsive or detecting mechanism but'which nevertheless permits the use of such driving means for the reciprocating carriage that the carriage may have variable and substantially uniform velocity throughout the whole of its strokes in opposite directions.

The above and other objects and advantages of the invention will become apparent upon consideration of the following specification and the accompanying drawing wherein there is disclosed a preferred embodiment of the invention.

In the drawing:

FIGURE 1 is a schematic showing of a control circuit utilizing the principles of my invention; and

FIGURE 2 is a fragmentary schematic showing the relation of certain proximity detectors utilized in the circuit of FIGURE 1 to a billet being scanned.

Referring first to FIGURE 2, reference numeral 22 represents an end View of a longitudinally advancing billet, 'and reference numeral 41 designates a reciprocating carrier for a double proximity detector 53 having an upper detector 56 and a lower detector 56. The detectors 56, 56, may be symmetrically disposed with respect to the working element (not shown, and which may also be carried by the reciprocating carriage 41), and in the above mentioned application of the invention this working element would be a pair of spaced defect search coils. In FIGURE 1, reference numeral 308 designates a coil of a solenoid which when energized moves the carriage 41 up to the left (FIG. 2) and when de-energized results in the movement of the carriage 41 down to the right. More specifically, carriage 41 may comprise a cylinder barrel in which a piston rod 41.1 is disposed to extend from opposite ends thereof. Rod 41.1 carries a piston disposed within the cylinder barrel, or carriage 41, and opposite ends of rod 41.1 are supported by suitable brackets 41.3. Piston rod 41.1 is hollow to provide for fluid flow from each end to adjacent respective sides of the piston 41.2. The arrangement is such that while the piston rod 41.1 is fixed against axial movement, the cylinder barrel, or carriage, is slidable therealong. Thus, if fluid pressure is admitted to the upper end of the piston rod 41.1, the carriage will be shifted upwardly and if fluid pressure is admitted to the lower end of the piston rod, the carriage will be shifted downwardly.

Conduits 41.4, 41.5 connect respective ends of piston rod 41.1 with respective outlet ports 41.6, 41.7 of a fluid valve 41.8 which is operated by the previously mentioned solenoid 30S. Valve 41.8 has an internal valve spool 41.9

connected with the solenoid 39S and an inlet port 41.10

and exhaust ports 41.11, 41.12. A spring 41.13 yieldably opposes operation of solenoid 30S, the latter, when energized, shifting the spool 41.9 against the force of spring 41.13 to the position shown wherein inletport 4.1.11) communicates with. outlet port 41.6 and wherein outlet port 41.7 communicates with exhaust port 41.12. When solenoid 308 is de-energized, spring 41.13 will shift the valve spool 41.9 to position wherein inlet port 41.10 communicates with outlet port 41.7 and outlet port 41.6 communicates with exhaust port 41.11. a

Byway of further preliminary explanation, the carriage 41 and accordingly the detector 53 may be mounted for movement toward 'andaway from the billet 22. When this is assembly is retracted in standby position the detector 56 is off the right edge of the billet, and by reason of the gap the detector 56 is also unaffected. As the assembly is brought down onto the billet, the detector 56 is affected to initiate operation of the apparatus as will be hereinafter explained.

Each of the proximity detectors 56 and 56' consists of a tapped search coil having a restricted magnetic core. The tap of coil 56' is connected to the cathode of an oscillator tubeVl through a variable resistor R3 while" one terminal of the coil is connected to the control grid of this tube by means of capacitor C1. These connec- The distributed capacitance between these conductors is utilized in conjunction with the inductance of the coil 56" to provide a tank oscillating circuit for oscillating tube V1. I provide a source of DC. voltage of the order of volts in the conductor 60 which voltage is impressed on the plate of tube V1 through an inductance L1 and resistance R1 in series. As shown, the control grid of tube V1 is also connected to ground through resistor R2, and the suppressor grid is also grounded while the screen grid is connected to ground through capacitor C2 and also to the juncture of inductance L1 and resistance R1. Ca pacitor C2 functions as an RF bypass while the inductance L1 serves as an RF choke.

The tube V1 oscillates at a frequency critical to the resonant circuit made up of the inductance of the coil 56' and the above mentioned distributed capacitance of the leads in the shielded cable SCI. As coil 56 nears the metal billet, its Q is lowered (shorted turns effect), and oscillation of tube V1 can no longer continue. The variable resistor R3 in the cathode circuit of tube V1 func- 3 tions as a sensitivity control in that it controls the strength of DC. plate current in the lower section of coil 56. By increasing resistance R3 the approach of a magnetic mass to the coil will have less effect on the change of bias on the control grid, necessitating closer coupling or spacing of the mass to the coil to extinguish the tube V1.

Coil 56 is similar in all respects to the coil 56' and is connected into the cathode-grid circuit of a second oscillator tube V2 in exactly the same manner as the coil 56' is connected to tube V1. The RF outputs of tubes V1 and V2 are connected through capacitors C6 and CS, respectively, and diodes D1 and D2, also respectively, to the control grids of sections A and B, respectively, of an amplifying tube V3, the plate voltages of which are supplied fro-m source 60 through resistors R10 and R9, respectively. The sections of tube V3 conduct so long as their connected oscillators are undalnped, and as will appear below there is provided a clamping or flip-flop circuit which operates to energize a first circuit as soon as one'section of tube V3 is extinguished and to hold this circuit energized until the other section is extinguished, and to similarly control a second circuit in vice versa manner.

Thus, in furtherance of the above, I provide the tube V4 having sections A and B with the anode of section A connected to the anode of section A of tube V3 by means of conductor 61 diode D5 It should be noted that the cathodes of tube V3 are connected to ground through diode D3 and that when section A of tube V3 is extinguished the potential on conductor 61 rises to approximately 135 volts. Likewise, the anode of section B of tube. V4 is connected to the anode of section B of tube V3 through conductor 62 and diode D4. Again, the potential in conductor 62 varies from about 55 volts when section B of tube V3 is conducting to about 135 volts 7 when this latter section is extinguished.

Referring now to the circuit connections for tube V4,

' it should be noted that the perspective anodes are crossconnected each through parallel resistance and capacitance to the control grid of the opposite section, with each control grid being connected to ground through a high resistance. The anodes of tube V4 are connected to source 60 through the respective resistors R11 and R12 and iaztlgodes thereof are connected to ground through resistor V4A and V4B form a bi-stable Eccles-Jordan circuit that can operate in any one of two stable conditions. In standby condition, however, wherein both oscillators are operating and both sections of amplifying tube V3 are conducting, both sections of tube V4 may also conduct simultaneously. As will appear hereinafter, this is of ad- 7 vantage in further holding otf subsequent control tubes and functions until the proximity sensinghead is brought down onto a billet. Thereafter V4A is on and V4B is ofl? or vice versa. The circuit is driven from one stable negative pulse to conductor 61 or 62. A sharp negative pulse to conductor 62 drives the grid of V4A negative causing it to go off. This same action increases the potential of conductor 61 driving the grid of V4B positive causing it to conduct. As V4B conducts, the potential of conductor 62 drops, clamping V4A in its off position. To drive the circuit back to its original state, a negative pulse on conductor 61 is required. Now as the anode potential of V3B increases from 55 v. to 135 v., a sharp positive pulse is delivered to conductor 62. Since V4A is on in its standby condition, this causes no action except to further keep V4B 011. As 56 approaches metal and oscillations cease in V1, the anode potential of V3A rises to 135 v. while conductor 61 remains at a lower potential 0t 45 v. as determined by V4A while in its on condition. This is the reverse biased condition on diode D5 and depicts its necessity. As long as anode V3A is at a greater positive potential than conductor 61, D5 cannot .conduct due to its high reverse resistance.

When coil 56 runs on the upper edge of the metal,

From theabove explanation, it should be apparent that at the start of the cycle of operation when the proximity sensing head 53 is brought from retracted position to place the coil 56 on the lower edge of the billet, oscillator V2 is extinguished. V3B also goes out allowing its anode to rise to volts and the voltage on conductor 62 will follow because of energization from source 60 through resistor R12. As will appear hereafter, this voltage appears in part at the control grid of a tube VSB causing it to increase its conduction and to initiate upward movement of the carriage 41. This rise in potential in conductor 62 greatly increases conduction in tube V4A, greatly lowering the drop across this tube section and locking out section B.

As the carriage 41 begins it upward movement, the lower proximity coil 56 also reaches the magnetic mass of the billet to terminate oscillation in tube V1 thus extinguishing conduction in section A'of tube V3. However, the resultant rise in voltage on the anode of V3A is unavailable to lift the voltage on conductor 61 because of the uni-directional nature of the diode D5, and accordingly the tube V4A-B remains stable. the upper coil 56 runs 011 the billet and tube V3B conducts will the tube V4 reverse. The rapid lowering of the voltage on the anode of V3B affects a negatively directed pulse in conductor 62 which, as explained above, extinguishes V4A, allowing V4B to conduct. Conduction in section B of tube V4 locks out section A thereof in the manner previously described for section B. An increase in conduction in section A of tube V5 raises the cathode potential of this section whichpotential is impressed on the control grid of a tube V7 to cause the same to conduct to energize a relay RV7 which is employed for control and/or indicating purposes not a part of the present invention. Decrease in conduction of section of B of tube V5 extinguishes tube V6 and deenergizes solenoid 36S whereby, in accordance with the above initial explanation the motive means for the carriage 41 is reversed to start the downward stroke of the scanning apparatus.

Again, as the downward stroke of the scanning apparatus proceeds a finite distance the upper coil 56 approaches the billet but the interlock provided by the tube V4 and connected circuitry prevents any control action until the lower coil 56' runs off the edge of the billet at which time the decrease in voltage in conductor 61 extinguishes conduction in section B of tube V4, allowing section A thereof to conduct. Also, conduction in section A of tube V5 is decreased and conduction section B is increased to dc-energize valve solenoid 308 to restart upward movement of the carriage 41. In this manner the reciprocation of the carriage for the scanning head continues so long asthe billet or other magnetic mass comes under the scanning head. When the cation in the manner described above.

The anodes of double tube V4 are connected to source 60 through resistors R11 and R12, respectively, while the cathodes thereof are connected to ground through resistor R23. The anodes of double tube V5 are connected direct to source 60 while the cathodes thereof are connected to ground through resistors R13 and R14,

Now the process repeats in the same manner,

Only when n respectively. Voltages in conductors 61 and 62 are impressed on the control grids of tube V5 by voltage dividing circuitscomprised of resistors R21, R22ground for section A; and resistors R19, R2tl-ground for sec tion B. Plate voltage for tubes V6 and V7 is provided by a positive source 63 of 200 volts, for example, while the cathodes of these tubes are connected direct to ground. Biasin'g potential for tube V6 is provided by a circuit comprised of ground, resistors R13, R25, R26, and source 64 of 150 volts negative, for example, with the control grid being tapped into the junction between R25 and R26. Normally the grid is at about 25 volts negative which is sufiicient to hold the tube off. However, when conduction in section B of tube V5 increases the rising voltage of its cathode, connected as shown, is suflicient to swing the voltage on this grid sufficiently positive to cause the tube to conduct. Tube V7 is controlled in the same manner.

From the above description, it should be now apparent that the system herein disclosed is essentially the combination of a set of parallel electronic relaying or amplifying circuits coupled with electronic means to hold a pair of interconnecting circuits in the system properly de-energized or reduced in energization for proper intervals of time all in accordance with the normal and expected pattern of reciprocation of a machine element whose reversal in stroke is to be directed by the apparatus of the disclosure. Thus, the function of the tube V4 and directly connected circuitry is to insure that only one channel is energized at a time and to provide in effect a reversing or memory device to energize a proper channel when a particular one of the sensing devices runs .olf the work. This is made possible by the use of two such devices, and a salient advantage of the system is that the stroke of the scanning apparatus may be automatically and electronically adjusted to a dimension of the workpiece.

It should now be apparent that I have provided an electronic control circuit for reciprocating scanners and the like which accomplishes the objects initially set out. Insofar as the directive control-to a valve solenoid, for example-is concerned there are no mechanical parts such as switches or relays, for example, which are troublesome and maintenance-prone in apparatus intended for substantially continuous operation and under the severe conditions of service normally encountered in industrial plants, particularly steel mills. Further, the control apparatus of this invention places no limitation on the speed of operation, and contributes materially to the design of the overall equipment with which the invention may be used because of the automatic tailoring of the length of stroke to the scanning dimension of the workpiece.

It should be apparent that if the direct reversing mechanism employedin the overall equipment to which the present invention is applied requires energization of a solenoid for movement in one scanning direction and the energization of a second solenoid for movement in the opposite direction the coil of relay RV7 may be employed for this latter purpose, the rocking tube V4 being available to insure the proper alternate energizations of such solenoids.

Having thus described my invention, what I claim is:

1. In combination: a carriage reciprocable from margin to margin of an electrically conductive workpiece, a pair of proximity devices carried by said carriage and spaced from each other in the direction of carriage reciprocation whereby in one direction of carriage movement'one of said proximity devices will be shifted beyond one workpiece margin and in the other direction of carriage movement the other sensing device will be shifted beyond the other workpiece margin, each proximity device forming a part of a respective oscillating circuit and each of such circuits oscillating when its associated proximity device is shifted beyond the margin of said workpiece and each circuit being dampened and ceasing to oscillate when its associated proximity device is adjacent said workpiece, and means responsive to oscillation in either of said circuits only while oscillation is dampened in the other circuit and such means interrupting carriage movement in one direction and elfecting carriage movement in the other direction when said one proximity device has been shifted beyond said one workpiece margin and interrupting carriage movement in the other direction and effecting carriage movement in said one direction when said other proximity device has been shifted beyond said other workpiece margin.

2. The construction of claim 1 and further comprising a scanning device carried by and reciprocable with said carriage for detecting defects in said workpiece.

3. The construction of claim 1 wherein said means 7 comprises an electronic switching circuit which has a pair of input circuits connected with the respective oscillating circuits and wherein said switching circuit also has an output circuit controlling carriage movement.

4. The construction of claim 3 wherein said output circuit controls an electromagnetically operated fluid valve, wherein said valve controls flow of fluid to a fluid motor, and wherein said motor effects carriage movement aforesaid.

References Cited by the Examiner UNITED STATES PATENTS 4/1959 Elam 317l47 X 2/ 1961 Frye 3l-8282 XR D. F. DUGGA-N, R. J. CORCORAN,

' 7 Assistant Examiners. 

1. IN COMBINATION: A CARRIAGE RECIPROCABLE FROM MARGIN TO MARGIN OF AN ELECTRICALLY CONDUCTIVE WORKPIECE, A PAIR OF PROXIMITY DEVICES CARRIED BY SAID CARRIAGE AND SPACED FROM EACH OTHER IN THE DIRECTION OF CARRIAGE RECIPROCATION WHEREBY IN ONE DIRECTION OF CARRIAGE MOVEMENT ONE OF SAID PROXIMITY DEVICES WILL BE SHIFTED BEYOND ONE WORKPIECE MARGIN AND IN THE OTHER DIRECTION OF CARRIAGE MOVEMENT THE OTHER SENSING DEVICE WILL BE SHIFTED BEYOND THE OTHER WORKPIECE MARGIN, EACH PROXIMITY DEVICE FORMING A PART OF A RESPECTIVE OSCILLATING CIRCUIT AND EACH OF SUCH CIRCUITS OSCILLATING WHEN ITS ASSOCIATED PROXIMITY DEVICE IS SHIFTED BEYOND THE MARGIN OF SAID WORKPIECE AND EACH CIRCUIT BEING DAMPENED AND CEASING TO OSCILLATE WHEN ITS ASSOCIATED PROXIMITY DEVICE IS ADJACENT SAID WORKPIECE, AND MEANS RESPONSIVE TO OSCILLATION IN EITHER OF SAID CIRCUITS ONLY WHILE OSCILLATION IS DAMPENED IN THE OTHER CIRCUIT AND SUCH MEANS INTERRUPTING CARRIAGE MOVEMENT IN ONE DIRECTION AND EFFECTING CARRIAGE MOVEMENT IN THE OTHER DIRECTION WHEN SAID ONE PROXIMITY DEVICE HAS BEEN SHIFTED BEYOND SAID ONE WORKPIECE MARGIN AND INTERRUPTING CARRIAGE MOVEMENT IN THE OTHER DIRECTION AND EFFECTING CARRIAGE MOVEMENT IN SAID ONE DIRECTION WHEN SAID OTHER PROXIMITY DEVICE HAS BEEN SHIFTED BEYOND SAID OTHER WORKPIECE MARGIN. 